Concentration of rare earths



United States Patent 3,089,759 CONCENTRATION OF RARE EARTHS Hugh J. Bronaugh, Chattanooga, and Paul R. Kruesr,

Signal Mountain, Tenn., assignors, by mesne assignments, to Vitro Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 18, 1960, Ser. No. 22,661 7 Claims. (Cl. 23-296) The present invention relates to the concentration of rare earth elements. More particularly it relates to th concentration of europium.

The usefulness of europium as a neutron absorbing material in the field of nuclear power has greatly increased the importance of this rare earth metal. It may be recovered by known and proven methods, such as the reduction of the tervalent ion to the divalent state and subsequent precipitation of europous sulfate, but this requires a feed material that has been previously enriched in europium to a value greater than that normally present in the ore. As the concentration of europium increases, a corresponding increase in recovery is obtained.

Although the classical methods of obtaining europium concentrates for subsequent recovery of europium tend to produce a fraction containing a higher concentration than the present procedure, these methods are laborious and time consuming. Good recoveries can be obtained according to the present invention with a concentrate containing a europium oxide to total oxide ratio of as little as 0.2%.

It is thus an object of the present invention to provide a simple, effective and speedy process for concentrating rare earth elements and particularly europium.

Another object is to obtain good recoveries of europium from a concentrate containing as little as 0.2% europium oxide.

These and other objects of the present invention will become apparent as the description proceeds.

In principle the present invention comprises heating a solution of rare earth chlorides at a temperature from about 190 F. to about 203 F. until a specific gravity of about 1.85 to about 1.92 is achieved, and then cooling the solution to a temperature of from about 149 F. to about 160 F. during a period of about 1 to about 3 hours to cause crystallization of the desired rare earth elements. According to such a process the rare earths with atomic numbers greater than 59, but including yttrium, are enriched in the crystals whereas, the lighter rare earths, lanthanum and cerium are concentrated in the mother liquor. The concentrated europium is then recovered from the crystals by known methods.

The mixed rare earth chlorides which are the starting material for the present process may be obtained by treating the mineral monazite, which consists predominantly of rare earth phosphates, with sodium hydroxide to form the rare earth hydroxides and then dissolving the latter compounds in hydrochloric acid. The mixed rare earth chloride crystals are then obtained by removing water from a dilute chloride solution containing rare earth cations until crystallization takes place.

The present process depends on the discovery that, contrary to expectations, the heavier rare earth elements are separated by selective crystallization on heating followed by rapid cooling. It is believed that this separation is due to the formation of an unstable crystalline hydrate. It is necessary, however, that the crystals be separated immediately; otherwise on standing, an equilibrium will be attained resulting in an ineffective separation.

The present process is applicable, as previously described, to solutions of mixed rare earth chlorides pro- 3,089,759 Patented May 14, 1963 duced as indicated herein, from monazite. It is equally applicable to the concentration of heavier rare earth metals from solutions of mixed rare earth cations which have previously been treated as described in copending patent application Serial No. 22,660, filed on even date herewith by Paul R. Kruesi, now United States patent number 3,089,758, and entitled Concentration of Rare Earths. According to said copending application, the mixed rare earth chlorides are first treated to obtain crystals enriched in the lighter rare earths, lanthanum, cerium and praseodymium. This is followed by a treatment to produce crystals enriched in the heavier rare earth metals. The mother liquor from this second treatment is then processed according to the method described herein to yield a crop of crystals further enriched in the heavier rare earth metals. These enriched crystals may in turn be dissolved in water and circulated through a bed of metallic zinc to reduce the europic ion to the europous ion. The addition of ammonium sulfate and barium ion to the solution containing the europous ions precipitates europous sulfate in a matrix of barium sulfate. The latter material may then be processed according to the method described in copending patent application Serial No. 22,834, filed on even date herewith by Hugh J. Bronaugh, and entitled Purification of Europium, to yield europium oxide having a purity of about 99.8% to 99.9%.

The following examples serve to illustrate the present invention without, however, limiting the same thereto.

EXAMPLE 1 Rare earth chloride crystals weighing 1,000 pounds were dissolved in approximately gallons of water in a steam-jacketed, glass-lined vessel. The solution was evaporated at a temperature of 194 F. until the specific gravity reached 1.92. The solution was then cooled to 154 F. during a specific time period of 1.5 hours. The crystals thus obtained were separated from the mother liquor by centrifugation.

The total rare earth content of the starting material was found to be 45.5%, calculated as oxides. The ratio of cerium, calculated as CeO to total oxide was 36%. The ratio of europium, calculated as Eu O to total oxide was 0.20%.

The product weighed 448 lbs. and had a total oxide content of 45.4%, of which the ratio of CeO to total oxide was 26.6% and the ratio of Eu O to total oxide was 0.34%.

The europium content of the starting material was (1000) (0.455) (0.002)=0.91 lb. while that of the product was (448) (0.454) (0.0034)=0.695 lb. Thus the percent recovery was EXAMPLE 2 1,092 lbs. of rare earth chloride crystals having a total oxide content of 45.5%, of which the cerium content, calculated as CeO was 36.2%, and of which the europium content calculated as Eu O was 21%, were treated at a temperature of 199 F. until the specific gravity was 1.90. They were then cooled to 151 F. for a period of about 2 hours. The separated crystals, weighing 480 lbs. had a total oxide content of 45.9%, of which the cerium content, as CeO was 28.2% and of which the europium content, as Eu O was 0.32%. Eu O in feed=1.04 lbs.; Eu O in product=0.71 1b.; percent recovery=68%.

A study of the cerium oxide to total oxide ratio in each of the cited examples will reveal that the product crystals are depleted in cerium. Thus the concentration of cerium has been increased in the mother liquor. Data obtained from several laboratory experiments set forth in the following table show the enrichment of various rare earth metals in the product crystals or the mother 4 at completion of the experiment is equal to the volume present in the crystallizer body at the start of the experiment. (2) The composition of the solution left in the crystallizer body at the completion of the experiment is equal liquor which is accomplished according to the present 5 process. to the composition of the solution present in the crys- ANALYSIS (WT. PERCENT R200) Y La Ir Nd Sm Eu Gd Tb Dy Ho Er Feed 5 40 0.0 20 0.1 0.22 4.1 0.4 2.3 0.2 0.25 50% Split:

Mother Liquor. 4.4 50 9 20 3.0 0.08 2.1 0.23 1.2 0.11 0.2

Crystals 5 5 27 10 40 8.7 0.3 0.5 0.5 3.0 0.25 0.3

EXAMPLE 3 tallizer body at the start of the experiment.

This example shows the application of the present proc- Mammal balance: ess to a rare earth mixture which has previously been 3g 353+4 4o3 treated according to the process described in the afore- W g2 mentioned copending application Serial No. 22,660. Europium balance. 5 13322 231:fif f gg gg l w f Feed: (39,915) (0.000s9)=35.5 lbs.

y perro corn lete c I th t '5 three (3) cr stallizations, was er- Cold crystals: (32353) (0'00044)=14'21bS' p Y e a 1 Y P formed each day. A typical procedure for one cycle is Hobho? crystals: (4403) (O'0042)=18'5 described as follows: Yleld CONCENTRATION OF RARE EARTHS 3Q 2 100=52% 1) Feed 1500 gallons of rare earth chloride solution to the crystallizer. Recovery (2) Concentrate solution by vacuum distillation at 160 3 F. until a specific gravity of 1.85 is obtained. 355 Q (3) Cool the solution slowly to 123 F. during a twelve Cerium balance.

(12) 110111" Perwd- Feed: 39,915 0.44ss =17,900 lbs. (4) Separate cold crystals by centrifugation, returning Cold crystals; (32,353) (0.4887)=15,800 lbs.

mother hquor to crystallize!" Hot-hot crystals: (4,403) (0.2476)=l,090 lbs. (5) Concentrate the solution in the crystallizer by vacu- 40 Yield, um distillation at 160 F. until a specific gravity of 1.35 to 1.90 is obtained. 15,800X 100:887 (6) Cool the solution to 158 F. and separate the hot 17,900 0 crystals as quickly as possible (crystals must be sepa- Balance:

rated within a. three (3) hour time limit). Return the mother liquor to the crystallizer. 16,890 X 1g0 94 4% (7) Recrystallize the hot crystals by dissolving them in 17,990

water, concentrating the solution by evaporation to a As many and varied modifications of the subject matspecific gravity of about 1.90 at a temperature of 195 ter of this invention will become apparent to those skilled F. Cool the mixture to 155 F. and separate the hotin the art from the detailed description given herein, it

h crystals b centrifugation, returning th th r should be understood that this invention is to be limited liquid to the vacuum crystallizen only in accordance with the appended claims.

What is claimed is: Table I presents 1111C data collected from this tell 1 A prgcess for the concentration of rare earth e1e day experiment. ments comprising heating a solution of chlorides of said elements at a temperature from about 190 F. to about 203 F. until the specific gravity is from about 1.85 to about 1.92, cooling said solution to a temperature of T able I from about 149 F. to about 160 F. during a period of CRYSTALLIZATION DATA. from about 1 to about 3 hours to cause crystallization of rare earth compounds with an increased content of Feed Cold Hot HOME compounds selected from the group consisting of yttrium Crystals Crystals C ys and rare earth elements having atomic numbers greater than 59, and immediately separating the crystals from 1001 Chloride Crystalslbs. 71,523 26,627 9, 699 the mother li u Wt. of R10 lbs. (Total Oxide) 30,015 32,353 12,233 4,403 2. A process for the concentration of europiurn com- 45 20 45 95 45 35 prising heating a solution of rare earth chlorides at a Average oiizl fififb'ere'eiiij "i if' 4sIs7 35130 24:70 temperature from about 190 F. to about 203 F. until AverageEuzoa/T-o-mment- M89 the specific gravity is from about 1.85 to about 1.92,

cooling said solution to a temperature of from about 1 Assumptions. 149 F. to about 160 F. during a period of from about 1 to about 3 hours to cause crystallization of said concentrated europium, and immediately separating the crystals from the mother liquor.

(1) The volume of solution left in the crystallizer body 3. A process according to claim 1 wherein the ratio of 5 europium to total rare earths expressed as the oxides is at least about 0.2% in the starting material and at least about 0.3% in the final crystals.

4. A process according to claim 1 wherein the ratio of europium to total rare earths expressed as the oxides is at least about 0.2% in the starting material and at least about 0.4% in the final crystals.

5. A process according to claim 2 wherein the ratio of europium to total rare earths expressed as the oxides is about 0.2% in the starting material and about 0.3% in the final crystals.

6. A process according to claim 2 wherein the ratio of europium to total rare earths expressed as the oxides is about 0.2% in the starting material and about 0.4% in the final crystals.

Schulze Sept. 10, 1935 Fleck May 7, 1940 OTHER REFERENCES Vickery: Chem. of the Lanthanums (1953), pages 110 to 123. 

1. A PROCESS FOR THE CONCENTRATION OF RARE EARTH ELEMENTS COMPRISING HEATING A SOLUTION OF CHLORIDES OF SAID ELEMENTS AT A TEMPERATURE FROM ABOUT 190*F. TO ABOUT 203*F. UNTIL THE SPECIFIC GRAVITY IS FROM ABOUT 1,85 TO ABOUT 1.92, COOLING SAID SOLUTION TO A TEMPERATURE OF FROM ABOUT 149*F. TO ABOUT 160*F. DURING A PERIOD OF FROM ABOUT 1 TO ABOUT 3 HOURS TO CAUSE CRYSTALLIZTION OF RARE EARTH COMPOUNDS WITH AN INCREASED CONTENT OF COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF YTTTIUM AND RARE EARTH ELEMENTS HAVING ATOMIC NUMBERS GREATER THAN 59, AND IMMEDIATELY SEPARATING THE CRYSTALS FROM THE MOTHER LIQUOR. 